Fusing apparatus

ABSTRACT

An apparatus in which a powder pattern deposited on a support material is permanently affixed thereto. The support material is heated during the movement thereof into thermal communication with a radiant energy output. In this manner, the powder pattern is coalesced and fixed permanently to the support material. 
     .[.The foregoing abstract is neither intended to define the invention disclosed in the specification, nor is it intended to be limiting as to the scope of the invention in any way..].

BACKGROUND OF THE INVENTION

This invention relates generally to an electrophotographic printingmachine, and more particularly concerns an apparatus for coalescing andaffixing permanently a powder pattern to a support material in imageconfiguration.

In the process of electrophotographic printing, a chargedphotoconductive member is exposed to a light image of an originaldocument to be reproduced for recording thereon an electrostatic latentimage. A development system, thereupon, moves a developer mix of carriergranules and toner particles, into contact with the photoconductivemember. Toner particles are attracted electrostatically to the latentimage forming a toner powder image thereon. The toner powder image is,then, transferred to the sheet of support material.

Multi-color printing repeats the foregoing process a plurality ofcycles. Each development cycle deposits differently colored tonerparticles on the support material, in superimposed registration with thepreviously deposited toner particles. Hence, the support material willhave transferred thereto various layers of toner particles forming amulti-layered powder image. The powdered layers have to coalesce andbecome transparent, i.e. each toner layer modulates the light rayspassing therethrough, to form a copy having a single composite color. Inthis manner, the modulated light rays transmitted through the tonerpowder layers are reflected from the support material back through thetoner powder to the eye of the observer. If the toner layers do notbecome transparent, the color reproduced will merely be that of theuppermost layer of toner particles. It is apparent that the fusingoperation must coalesce the toner particles and form transparent layersthereof to appropriately modulate the light rays transmittedtherethrough creating a copy having the composite color of the originaldocument.

Generally, the toner particles include, primarily, fusible resins. Whensuch toner particles are transferred to the support material, the powderimage can be permanently affixed thereto by heating which partiallydissolves the toner particles causing them to fuse into the supportmaterial. Conventional black and white electrophotographic printingmachines utilize fusers which heat the toner particles sufficiently tofix them to the support material, while not charring or igniting thesupport material. Heretofore, there was little concern with coalescingmulti-layers of toner particles. Thus, it is apparent that therequirement for coalescing multi-layers of toner particles adds but onemore variable in an already complex system.

Preferably, it is desirable to raise the temperature of the supportmaterial so that it is close to the fusing temperature of the tonerparticles. In this way, the support material acts as a heat sourcerather than a heat sink during the fusing operation. Thus, a suitablefusing apparatus may include heating the support material as well asapplying radiant heat thereto to permanently affix and coalesce thetoner powder image to the support material.

Heating of the support material prior to exposing the toner powder imageto radiant energy has been disclosed in U.S. Pat. No. 3,187,162 issuedto Toku Hojo et al. in 1965. As disclosed therein, the support materialadvances over a pre-heat platen which raises the temperature thereof byconduction. The fuser disclosed in the Hojo patent also includes anincandescent filament lamp arranged adjacent to and over the path oftravel of the support material to emit radiant energy which assists infusing the toner powder image to the support material.

In high speed electrophotographic printing machines, the utilization ofa stationary pre-heat platen may pose a problem. A boundary layer of airfrequently is developed between the rapidly moving support material andthe pre-heat platen. This layer of air serves to insulate the supportmaterial from the pre-heat platen and introduces a variable in theactual temperature of the support material. The more rapidly the supportmaterial is moved over the platen, the greater the uncertainty inheating the support material to a predetermined temperature. This isparticularly significant when the support material is cut sheet paper,such as is used in conventional electrophotographic printing machines,rather than a web of paper passing over the pre-heat platen. The rapidmovement of a relatively non-rigid sheet forces air between the heatedplaten and the sheet. Hence, the more rapidly the cut sheet of papermoves over the heated platen, the greater will be the boundary layercreated thereby. In addition thereto, the radiant heater and thepre-heat platen must operate in conjunction with one another to coalesceand affix the multi-layer toner powder image to the support material.This should be achieved without charring or igniting the supportmaterial. Precise temperature control of the support material is notreadily attainable when a sheet of cut paper passes over a stationaryplaten forming a layer of air therebetween.

Accordingly, it is a primary object of the present invention to improvethe fusing of single or multi-layered toner powder images to create acomposite colored reproduction corresponding to the original coloreddocument.

SUMMARY OF THE INVENTION

Briefly stated, and in accordance with the present invention, there isprovided an apparatus for coalescing and affixing permanently a powderpattern to a support material.

In the preferred embodiment thereof, the apparatus includes transportmeans, heating means, and a radiant energy source. The transport meansadvances a sheet of support material with a powder pattern deposited onone surface thereof along a path of movement, the other surface of thesupport material being in substantial contact with the transport means.As the support material is advanced, heating means heat the transportmeans, which, in turn , heats the support material. Additional energy issupplied by the radiant energy source, the radiant energy source beingin thermal communication with the support material advancing along thepath of movement thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will becomeapparent upon reading the following detailed description and uponreference to the drawings, in which:

FIG. 1 is a schematic perspective view of an electrophotographicprinting machine having the present invention therein;

FIG. 2 is a perspective view of the fuser incorporated in the FIG. 1printing machine with the cover pivoted to the opened position;

FIG. 3 is a perspective view of the FIG. 2 fuser;

FIG. 4 is a plan view of the cover utilized in the FIG. 2 fuser;

FIG. 5 is a plan view of the FIG. 2 fuser bottom housing; and

FIG. 6 is a sectional elevational view taken along the line 6--6 of FIG.5 in the direction of the arrows.

While the present invention will be described in connection with thepreferred embodiment and method of use thereof, it will be understoodthat it is not intended to limit the invention to that embodiment ormethod of use. On the contrary, it is intended to cover allalternatives, modifications and equivalents as may be included withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF INVENTION

In an electrophotographic printing machine, very little time isavailable in which to coalesce and affix permanently a multi-layeredpowder image to a support material. The heat transfer must be rapidlyand efficiently accomplished to obtain complete coalescence. Radiantheat transfer, in which infrared energy is emitted from a hightemperature source, is an efficient source of energy which can bereadily transferred to a support material having a multi-layered tonerpowder image deposited thereon.

An efficient radiator of infrared energy converts a high percentage ofthe internal energy available to radiant heat, and will concentrate thisenergy in a band of wavelengths located at the short end of the infraredspectrum. The support material is generally paper which absorbs a highpercentage of infrared energy at wavelengths greater than 3.0 microns.At shorter wavelengths, the infrared energy absorption of the paperdecreases rapidly. Infrared energy incident upon the toner powder imageis rapidly converted to internal energy. However, if the temperature ofthe support material is lower than that of the toner powder image, thesupport material will act as a heat sink dissipating heat from the imageareas. The heat energy transferred conductively from the toner powderimage to the support material is dependent upon the temperature gradienttherebetween. The magnitude of this heat transfer is critical, and mayprevent the coalescence of the multi-layered toner powder image utilizedin color electrophotographic printing. It, therefore, appears to bedesirable to heat the support material minimizing any heat loss thereto.In the present invention, the support material is heated, in conjunctionwith, radiant energy being supplied thereto to coalesce the toner powderimage. This will be explained in greater detail with reference to thedrawings wherein like reference numerals have been used throughout todesignate like elements.

Turning now to the drawings, FIG. 1 schematically illustrates anelectrophotographic printing machine arranged to produce multi-colorcopies from a color original. As shown therein the machine employs aphotoconductive member having a rotatably mounted drum 10 with aphotoconductive surface 12 thereon. Drum 10 rotates in the directionindicated by arrow 14 to move photoconductive surface 12 through aseries of processing stations A through E, inclusive.

Initially, drum 10 rotates photoconductive surface 12 through chargingstation A which has a corona generating device, indicated generally bythe reference numeral 16, positioned thereat. Preferably, coronagenerating device 16 extends transversely across photoconductive surface12 and is arranged to charge surface 12 to a relatively high uniformpotential. A suitable corona generating device is described in U.S. Pat.No. 2,778,946 issued to Mayo in 1957.

Charged photoconductive surface 12 next rotates to exposure station Bwherein a moving lens system, indicated generally at 18, and a colorfilter mechanism, depicted generally at 20, are positioned. One type ofmoving lens system suitable for the electrophotographic printing machineof FIG. 1 is disclosed in U.S. Pat. No. 2,062,108 issued to Mayo in1962. As illustrated in FIG. 1, a colored original document 22 isstationarily supported face down upon transparent viewing platen 24. Inthis manner, successive incremental areas of original document 22 areilluminated by a moving lamp assembly, indicated generally at 26. Lampassembly 26 and lens system 18 are moved in a timed relation with drum10 to produce a flowing light image of original document 22 onphotoconductive surface 12. The resultant image produced onphotoconductive surface 12 is termed an electrostatic latent image. Theelectrophotographic printing machine depicted in FIG. 1 is arranged tointerpose selected colored filters in the optical path of lens 18 viafilter mechanism 20. Preferably, filter mechanism 20 operates on thelight rays transmitted through lens 18 to record an electrostatic latentimage on photoconductive surface 12 corresponding to a preselectedspectral region of the electromagnetic wave spectrum, i.e. a colorseparated electrostatic latent image. In this manner, an electrostaticlatent image is produced on photoconductive surface 12 which correspondsto a single color of original document 22.

Subsequent to the recording of the color separated electrostatic latentimage on photoconductive surface 12, drum 10 rotates to developmentstation C having three individual developer units, generally indicatedby the reference numerals 28, 30 and 32, respectively, located thereat.The developer units depicted in FIG. 1 are all magnetic brush typedeveloper units. In a magnetic brush development system, a magnetizabledeveloper mix having carrier granules and toner particles is continuallybrought through a directional flux field to form a brush of developermix. A suitable development system utilizing a plurality of developerunits is disclosed in copending application Ser. No. 255,259 filed in1972. Development is achieved by contacting photoconductive surface 12with the brush of developer mix. Developer units 28, 30 and 32, eachapply toner particles corresponding to the complement of the colorseparated latent image recorded on photoconductive surface 12. Forexample, developer units 28 deposits cyan toner particles on a redfiltered latent image, developer unit 30 deposits magenta tonerparticles on a green filtered latent image, and developer unit 32deposits yellow toner particles on a blue filtered latent image. Theaforementioned steps of depositing various color toner particles on therespective electrostatic latent images occurs sequentially rather thansimultaneously.

After development, the toner powder image electrostatically adheres tophotoconductive surface 12 and moves therewith to transfer station D. Attransfer station D the powder image is transferred to a sheet of finalsupport material 34 by means of a biased transfer roll, shown generallyat 36. U.S. Pat. No. 3,612,677 issued to Langdon in 1972 discloses asuitable electrically biased transfer roll. Transfer roll 36 is biasedelectrically to a potential such that the magnitude and polarity thereofis sufficient to attract electrostatically the toner powder image fromphotoconductive surface 12 to support material 34. A single sheet ofsupport material 34 is supported on transfer roll 36. Bias transfer roll36 is arranged to recirculate the sheet of support material 34 insynchronism with the rotation of drum 10. In this manner, the tonerpowder images developed on photoconductive surface 12 are transferred,in superimposed registration, to sheet 34. Hence, it is apparent that ina multi-color electrophotographic printing of the type depicted in FIG.1, the aforementioned steps of charging, exposing, developing andtransfer are repeated for a plurality of color separated light images inorder to form a composite picture of the original document correspondingin color thereto.

After the last transfer operation, support sheet 34 is stripped frombias transfer roll 36. Conveyor 60 advances sheet 34 to a fuser, showngenerally at 38, where the multi-layered toner powder image is coalescedand permanently affixed thereto. Fuser 38 will be discussed hereinafterin conjunction with FIGS. 2 through 6, inclusive, in greater detail.After the multi-layered toner powder image is coalesced to supportmaterial 34, endless conveyor belts 40 and 42 advance support material34 to catch tray 44 for subsequent removal by the machine operator.

Cleaning station E is the last processing station in the direction ofrotation of drum 10, as indicated by arrow 14. Cleaning station E haspositioned thereat a rotatably mounted fibrous brush 46 which engagesphotoconductive surface 12 to remove residual toner particles remainingthereon after the transfer operation. Preferably, fibrous brush 46 is ofthe type described in U.S. Pat. No. 3,590,412 issued to Gerbasi in 1971.

It should be noted that support material 34 may be plain paper or atransparent thermoplastic sheet, amongst others, which is advanced froma stack 48 mounted on tray 50. Feed roll 52 separates and advances theuppermost sheet from stack 50 into a baffle arrangement 54. Baffle 54guides the advancing sheet into the nip of a pair of register rollswhich align the sheet and pass it therebetween such that it isreleasably secured to bias transfer roll 36. Bias transfer roll 36 isarranged to rotate in the direction of arrow 58 moving support material34, releasably secured thereto, in a recirculating path such thatsuccessive toner images are transferred thereto in superimposedregistration with one another forming a multi-layered toner powderimage.

Referring now to FIG. 2, there is shown a perspective view of the fuserutilized in the electrophotographic printing machine of FIG. 1. Thefuser is depicted in FIG. 2 as having the cover pivoted to an openposition. Conveyor 60 is associated with the fuser to transport supportmaterial 34 from transfer roll 36 thereto. Conveyor 60 comprises aplurality of endless belts 62 entrained about a pair of opposed, spacedrollers 64. A vacuum system maintains a low pressure by drawing airthrough apertures 66 in belt 62 to tack support material 34 thereto.Leaf switch 68 detects the presence of support material 34 on belt 62and indicates that support material 34 has been stripped properly frombias roll 36 without causing a machine jam. A suitable timing disc (notshown), mounted on drum 10 and adapted to rotate, therewith cooperateswith the machine logic to actuate fuser 38 when sheet 34 passes therein.Fuser 38 is mounted slidably in the electrophotographic printingmachine, i.e. it is mounted on a pair of spaced slides 70 and 82 affixedto the frame of the machine. This permits the removal of the fuser andthe repair or replacement thereof.

As depicted in FIG. 2, fuser 38 includes a cover member 74 pivoted tothe opening position to show more clearly lower housing member 76. Covermember 74 includes radiant energy source 78 which will be described ingreater detail with reference to FIG. 4. Handle 81 is adapted to pivotcover 74 from the open position, as shown in FIG. 2, to the closedposition of FIG. 3. Latch 80 disengages fuser 38 from the printingmachine frame permitting the removal thereof along slides 70 and.[.82.]. .Iadd.72.Iaddend.. Lower housing member 76 defines an openended chamber having a pair of spaced rollers 82 and 84 mountedrotatably on transport frame 109 (FIG. 5) disposed therein. An endlessbelt 86 is entrained about rollers 82 and 84. Endless belt 86 includes aplurality of apertures 88 therein which are arranged to draw airtherethrough such that support material 34 is tacked thereto as itpasses through fuser 38. Preferably, endless belt 86 is made from anelastomeric material such as silicone rubber. However, any flexiblematerial having high thermal resistance may be suitable.

Referring now to FIG. 3, there is shown fuser 38 with cover member 74 inthe closed position. As illustrated therein, cover member 74 is pivotedin the closed position. When closed, cover member 74 in conjunction withlower housing member 76, defines a passage way through fuser 38permitting endless belts 62 and 86 to move support material 34therethrough. Fuser 38 includes a male connector 90 adapted to mate witha female connector (not shown) mounted on the frame of the printingmachine. This enables fuser 38 to readily be removed from the machineand re-installed therein without connecting electrical wires, i.e. fuser38 moves along slides 72 and .[.74.]. .Iadd.70 .Iaddend.until connector90 mates with the female connector mounted on the machine frame. Thiselectrically connects the fuser to the power supply placing it in anoperable mode. Air removing means or blower motor 92 is operativelyassociated with fuser 38 to maintain a suitable pressure differentialtacking support material 34 to the exterior surface 86a of endless belt86. In addition thereto, the air passing through endless belt 86 isheated. The heating means will be described hereinafter in conjunctionwith FIGS. 5 and 6. Preferably, blower motor 92 is a two-polesplit-capacitor motor.

Turning now to FIG. 4, there is shown a planar view of cover member 74.Preferably, cover member 74 includes a metal shell having secured to theinterior surface thereof suitable insulation. A silicon rubber coatingis sprayed on the exterior surface of cover 74 to protect the operator.An outer reflector 94 is suitably secured to the insulation. An innerreflector 96 is mounted to the outer reflector via a pair of screws 98.Both reflectors 94 and 96, preferably, are made from aluminum having areflectivity of approximately 95 percent. Air circulates between innerreflector 96 and outer reflector 94. Sensing means or a thermistor ispositioned in the air space between inner reflector 96 and outerreflector 94 to measure the temperature thereat. One type of suitablethermistor for detecting the temperature in the air space between outerreflector 94 and inner reflector 96 is a glass bead thermistor.

The radiant energy source or radiant heat strip 78 is a nickel chromiumalloy ribbon 100 entrained helically between a pair of spaced opposedsupport members such as ceramic spool assemblies 102 and 104,respectively. The arrangement of heat strips 78 is such as to providesubstantially uniform radiation therefrom. Heat strips 78 are of a lowthermal mass, preferably, being made from a nickel chromium alloy, andhaving the end elements thereof arranged to prevent radiation fall off.Ceramic spool 102 is mounted fixedly to cover 74. Ceramic spool 104 ismounted to a leaf spring arrangement 106 which, in turn, is mountedfixedly on cover 74. Leaf spring 106 is made from a high temperaturesteel and is adapted to permit the distance between ceramic spools 104and 102 to vary as a function of the thermal expansion of nickelchromium alloy ribbon 100. A suitable guide, preferably wire 108, iswound over energy source 78 and arranged to prevent support material 34from engaging the heating elements or nichrome ribbon 100. Guide 108 maybe made from nichrome wire, fiberglass string, or, preferably, fromquartz string.

Turning now to FIG. 5, there is shown a plan view of lower housingassembly 76. Lower housing 76 includes a sheet metal shell 110 havinginsulation secured to the interior surface thereof. Transport frame 109is mounted removably in shell 110. Rollers 82 and 84 are rotatablymounted on frame 109 and have entrained thereabout endless belt 86.Interior surface 86b of endless belt 86 is adapted to engage platemember 112. Plate member 112 includes a plurality of apertures or slots114 therein adapted to permit the flow of air therethrough in thedirection of arrows 116. Blower member 92 has vane member 118 mountedthereon and is adapted to rotate vane member 118 such that air flows inthe direction of arrows 116. The air flow passes over heating means orauxiliary heater 120 onto plate member 112 raising its temperature.Plate member 112 engages the undersurface 86b of endless belt 86 andconducts heat thereto. This, in turn, raises the temperature of supportmember 34 minimizing any heat loss thereto. In this manner, radiantenergy from elements 110, in conjunction with the heated supportmaterial 34 coalesces the multi-layered toner powder image formedthereon.

Referring now to FIG. 6, there is shown a sectional elevational view ofthe air flow in lower housing 76. As shown therein, air moves downwardlythrough the exterior surface 86a of endless belt 86 in the direction ofarrow 122. It passes through the opened ends of endless belt 86 asindicated by arrow 124 and over the resistance heating elements 126 ofheating means 120 as indicated by arrow 128. It is drawn into vanemember 118 as shown by arrow 130, and propelled therefrom, as indicatedby arrows 132 and 134, onto plate member 112 contacting interior surface86b of endless belt 86. Heating means 120 is, preferably, a 800 watttubular high mass heater. Sensing means of a cam enclosed beadthermistor (not shown) is arranged to detect the temperature of endlessbelt 86. The thermistor is mounted on a thermally conductive shoe which,in turn, is arranged to contact the lower surface 86b of belt 86.

The control means for heating means 120 is, preferably, a timeproportional, zero cross-over controller whose function is to maintainthe temperature of endless belt 86 at a prescribed standby temperature.Temperature control is achieved through thermistor feedback. The beltthermistor measures the actual temperature of belt 86 and suitablecomparator circuits compare the sensed temperature with a referencecorresponding to the desired standby temperature. The comparatorcircuits develop an error signal for actuating heating means 120. Inthis way, endless belt 86 is maintained at a desired standbytemperature. The radiant energy source controller provides the controlfor radiant heat strip 78. It furnishes two distinct power levels, i.e.1,750 watts and 1,250 watts, which are dependent upon the airtemperature between outer reflector 94 and inner reflector 96. Asmentioned previously, the thermistor positioned thereat detects thetemperature in the air space therebetween. Preferably, the switch pointis about 450° F. thus, if the thermistor positioned in the air spacebetween inner and outer reflectors 96 and 94, respectively, indicates atemperature greater than 450° F switching means changes the power inputto radiant strips 78 from about 1,750 watts to about 1,250 watts. If thethermistor indicates a temperature less than 450° F, the power input toradiant strips 78 switches from about 1,250 watts to about 1,750 watts.This is achieved by suitable comparator circuits which compare themeasured temperature, as indicated by the thermistor in the air spacetherebetween, with a reference. The difference is an error signal whichis utilized to control radiant strips 78. The foregoing type of controlarrangement is utilized to maintain the total radiation impinging thepowder image substantially constant. It is evident that as thetemperature of both reflectors increases, the radiation emittedtherefrom also increases. Thus, in order to maintain the total emittedradiation substantially constant, it is necessary to reduce theradiation emitted from heat strip 78. This is accomplished by reducingthe power furnished to heat strip 78 from about 1,750 watts to about1,250 watts.

In operation the electrophotographic printing machine is turned on andheated from a cold condition to a standby condition. During the warm upphase both heating means 120 and radiant energy source 78 are activated.Initially radiant energy source 78 operates a a full power of 1,750watts. When endless belt 86 is raised to a preselected standbytemperature which may range from about 390° F to about 420° F, dependingupon humidity conditions, radiant energy source 78 is turned off. Fuser38 is maintained at the standby temperature by heating means 120. When asheet of support material enters the fuser the machine logic energizesradiant energy source 78 at the upper power level (in this case 1,750watts), and de-energizes heater 120. As the sheet of support materialleaves the fuser, the machine control logic energizes heater 120 andde-energizes radiant energy source 78. The preceding control schemecontinues if the thermistor positioned in the air space between outerreflector 94 and inner reflector 96 indicates a temperature below about450° F. If, however, the temperature exceeds about 450° F, radiantenergy source 78 is energized at a lower power level (in this case 1,250watts) when a sheet of support material enters the fuser. In additionthereto, heater 120 is energized substantially simultaneously withradiant energy source 78. As the sheet of support material leaves thefuser, the machine control logic de-energizes radiant energy source 78,while heater 120 remains energized. Furthermore, in the event that atransparency material such as a coated thermoplastic material ratherthan a paper is passing through the fuser, energy source 78 isinactivated and heating means 120 is activated. Thus, it is apparentthat the aforementioned fuser and the associate control mechanismmaintain the support material and the environment surrounding themulti-layered toner material at a sufficient temperature to coalesce thepowder image without igniting or charring the support material.Therefore, it is apparent that the fusing apparatus of the presentinvention coalesce a multi-layered toner powder image creating acomposite color reproduction corresponding to the original coloreddocument.

In recapitulation, sequential color separated electrostatic latentimages are formed on a photoconductive surface and sequentiallydeveloped by the respective colored toner particles complementing thecolor separated latent image. The developed toner powder image istransferred to a sheet of support material. This process is repeated aplurality of times forming a multi-layered (in this case a threelayered) toner powder image wherein each layer of toner powder is of adistinctly different color from the prior layer. The layers of tonerpowder are coalesced in the fuser of the present invention forming acomposite multi-color reproduction affixed to a support material.

Thus, it is apparent that there has been provided, in accordance withthis invention, a fusing apparatus that fully satisfies the objects,aims and advantages set forth above. While the invention has beendescribed in conjunction with a specific embodiment and method of usethereof, it is evident that many alternatives, modifications andvariations will be apparent to those skilled in the art in light of theforegoing description. Accordingly, it is intended to embrace all suchalternatives, modifications and variations as fall within the spirit andbroad scope of the appended claims.

What is claimed is: .[.1. An electrophotographic printing machine of thetype having a powder pattern formed on a sheet of support material,wherein the improvement includes: pattern to the sheet of supportmaterial..].
 2. .[.A printing machine as recited in claim 1, furtherincluding:.]. .Iadd.An electrophotographic printing machine of the typehaving a powder pattern formed on a sheet of support material, whereinthe improvement includes:means for transporting the sheet of supportmaterial with the powder image deposited on one surface thereof along apath of movement, said transport means being arranged to be insubstantial contact with the other surface of the sheet of supportmaterial; means for heating said transport means; a radiant energysource having at least one heat strip arranged to be in thermalcommunication with the sheet of support material for supplying theenergy output thereof onto the sheet of support material being movedwith the powder pattern thereon by said transport means along the pathof movement coalescing and affixing substantially permanently the powderpattern to the sheet of support material; .Iaddend. first control meansarranged to actuate said heating means in response to the printingmachine being energized for rapidly heating and regulating saidtransport means at about a standby temperature; and second control meansarranged to actuate said radiant energy source, in response to theprinting machine being energized, for rapidly heating said transportmeans to about the standby temperature; and deactuating said radiantenergy source at about the standby temperature, said second controlmeans, responsive to the sheet of support material being positioned onsaid transport means, for regulating said radiant energy source about apredetermined temperature at a lower power level and below thepredetermined temperature at a higher power level.
 3. A printing machineas recited in claim 2, wherein said second control means includes:meansfor sensing the temperature in the region of said radiant energy sourceand generating an electrical output signal corresponding thereto; meansfor developing a reference corresponding to the predeterminedtemperature; means for comparing the electrical output signal with thereference to generate an electrical error signal indicative of thedifference therebetween for regulating the power output from saidradiant energy source; and means for switching said radiant energysource to the lower power level from the higher power level in responseto the electrical error signal from said comparing means indicating saidsensing means being above the predetermined temperature.
 4. A printingmachine as recited in claim 2, wherein said first control meansincludes:means for sensing the temperature in the region of saidtransport means and generating an electrical output signal correspondingthereto; means for developing a reference corresponding to the standbytemperature; and means for comparing the reference with the electricaloutput signal and generating an electrical error signal indicative ofthe difference therebetween for regulating the power from said heatingmeans.
 5. A printing machine as recited in .[.1.]. .Iadd.2.Iaddend.wherein said transport means includes:a lower housing memberdefining an interior open ended chamber; a frame member mountedremovably in the chamber of said lower housing member; a plurality ofrollers mounted rotatably on said frame member, said rollers beingpositioned spaced from one another and having the axes of rotationthereof substantially parallel to one another; an endless belt memberhaving a plurality of apertures therein, said belt member beingentrained about said rollers; and means for removing air from thechamber of said lower housing to secure releasably the sheet of supportmaterial to the exterior surface of said belt member.
 6. A printingmachine as recited in claim 5, wherein said endless belt memberpreferably is made from a high temperature elastomer. . A printingmachine as recited in claim 5, wherein said heating means includes:aplate member having a plurality of apertures therein, said plate memberbeing mounted in the open end of the chamber of said lower housinginterposed between said rollers and substantially contacting theinterior surface of said belt member; and at least one resistanceheating element disposed in the chamber of said lower housing member,said heating element being positioned in the path of movement of the airbeing removed from the chamber heating the air which heats said beltmember.
 8. .[.A printing machine as recited in claim 5, wherein saidradiant energy source includes:.]. .Iadd.An electrophotographic printingmachine of the type having a powder pattern formed on a sheet of supportmaterial, wherein the improvement includes:a lower housing memberdefining an interior open-ended chamber; a frame member mountedremovably in the chamber of said lower housing member; a plurality ofrollers mounted rotatably on said frame member, said rollers beingpositioned spaced from one another and having the axes of rotationthereof substantially parallel to one another; an endless belt memberhaving a plurality of apertures therein, said belt member beingentrained about said rollers; means for removing air from the chamber ofsaid lower housing to secure releasably the sheet of support material tothe exterior surface of said belt member; .Iaddend. a cover membermounted on said lower housing member and defining with said lowerhousing member a passage way enabling said endless belt member to movesupport material therethrough; at least one radiant heat strip securedto said cover member, said heat strip being configured to furnishsubstantially uniform radiation across the surface of the sheet ofsupport material; and reflecting means interposed between said covermember and said radiant strip directing the energy output therefrom ontothe support material to coalesce and permanently affix the powderpattern thereto.
 9. A printing machine as recited in claim 8, whereinsaid heat strip is preferably made from a helically wound ribbon of lowthermal mass.
 10. A printing machine as recited in claim 9, furtherincluding a pair of opposed spaced support members having said helicalribbon entrained thereabout, one of said support members being mountedsubstantially fixedly on said cover member and the other of said supportmembers being mounted resiliently on said cover member to compensate forthermal expansion of said helical ribbon. . A printing machine asrecited in claim 8 wherein said heat strip is preferably made from hightemperature nickel chromium alloy.